In the manufacturing of integrated circuits, design kits are needed to monitor process variations in order to ensure that the electrical performance of the integrated circuits is within specifications. The design kits may include metal-over-metal (MOM) capacitors designed in scribe lines of wafers.
In conventional MOM capacitor design kits, a MOM capacitor extends from the bottom metal layer to the top metal layer of the respective wafer. Two ports are formed at the surface of the wafer and connected to the two capacitor plates of the MOM capacitor. The measured capacitance and resistance may reflect the process variations in the manufacturing of the wafer.
In the integrated circuit manufacturing processes, residue moisture may undesirably remain in extreme-low-k dielectric layers, in which metal layers are formed. The residue moisture plays an important role in the performance of the MOM structure. The property of one metal layer may thus affect the overall performance of integrated circuits significantly, and hence the metal layer may need to be identified. However, the conventional MOM capacitor design kit can only be used to find the overall process variations of all metal layers. The process variation in each of the metal layers cannot be reflected. Accordingly, the specific metal layer causing the process variation reflected by the measurement result cannot be identified. Further, conventional MOM capacitor design kit takes large chip area, and is not efficient in the usage of the chip area.